Follow-up: So my bass player has expressed interest in playing guitar moving forward. He plays guitar in my old band "Empyrean Plague" so I know he and I could write/play some heavy riffs together. He also has a 5150/mesa 412 so I don't have to worry about tone/volume. I'm thinking that he and I will weave some Heavy AF riffs together with some limited 'lead' work, and I'll record the bass and play it via backing track. We already use backing tracks for the 1st album strings/synth/piano material, so we're all set to use it for bass.